1. Field of the Invention
This invention relates generally to semiconductor processing, and more particularly to a circuit structure incorporating a photosensitive anti-reflective coating and to methods of making the same.
2. Description of the Related Art
The fabrication of modern integrated circuits requires the patterning of millions of different types of regions on a semiconductor wafer, such as local interconnect trenches, global metallization layers, and transistor gates, to name just a few. The manufacture of such multitudes of tiny structures is made possible by the use of lithographic processing. In photolithographic processing, a layer of photoresist material is applied to the wafer, frequently by spin-coating. Next, the photoresist layer is exposed to an actinic radiation source, such as ultraviolet (xe2x80x9cUVxe2x80x9d). The UV radiation is first passed through a mask or reticle that selectively passes some of the UV radiation while blocking other portions so that only preselected portions of the photoresist are exposed to the radiation. The radiation changes the chemical character of the photoresist, either rendering it soluble or insoluble in a subsequent solvent step, depending upon whether the resist is negative-tone or positive-tone photoresist. The resist is then developed by exposure to a developer solvent. The areas of the photoresist remaining after the development step mask and protect the substrate regions that they cover.
The quality of the developed image depends on, among other things, the optical properties of the resist and the films underlying the resist. In amorphous and polysilicon patterning, oxide films frequently underlie the deposited poly or amorphous film. Highly reflective films, such as polysilicon, metals and oxides tend to reflect significant quantities of radiation back upward and into the resist. This reflected radiation can produce interference patterns within the resist that impact the quality of the image.
During exposure of the mask resist, reflection from the substrate may result in so-called xe2x80x9cfootingxe2x80x9d in the edges of the patterned resist openings. In order to suppress the effects of reflected light, a bottom anti-reflective coating (xe2x80x9cBARCxe2x80x9d) is commonly formed underneath the photoresist layer. The composition of the BARC is selected to be highly absorbing at the exposure wavelength for the photoresist. In one conventional fabrication process, a silicon nitride or oxynitride film is used as a BARC. A photoresist film is applied to the BARC, exposed and developed to uncover portions of BARC. Prior to, additional fabrication steps, such as ion implantation or etching, the uncovered portions of the BARC must normally be removed. This is frequently done with reactive ion etching (xe2x80x9cRIExe2x80x9d) in order to achieve anisotropic removal. However, RIE subjects the substrate and any circuit structures formed thereon to kinetic bombardment, which can damage critical structures. Wet etching may be used to etch the BARC with lower risk of substrate damage. However, wet etching proceeds isotropically, resulting in undercut of the overlying resist film. If the undercut is severe enough, the resist can lift off.
Another conventional resist process utilizes a polymer-based BARC material that is not photosensitive but is soluble in the resist developer solution. The polymer-based BARC layer is deposited and pre-baked. A resist film is next applied and patterned. The mask pattern is transferred to the BARC during the development step following exposure. This occurs because the BARC polymer material dissolves in the presence of the resist developer solvent. The dissolution of the polymer-based BARC proceeds isotropically at a removal rate that is dependent on the pre-bake conditions. If the pre-bake is deficient, significant undercut of the BARC can occur during resist development and lead to resist lift-off.
The present invention is directed to overcoming or reducing the effects of one or more of the foregoing disadvantages.
In accordance with one aspect of the present invention, a circuit structure is provided that includes a substrate and a first photosensitive film on the substrate. The first photosensitive film is photosensitive to a first electromagnetic spectrum and anti-reflective of a second electromagnetic spectrum that differs from the first electromagnetic spectrum. A second photosensitive film is on the first photosensitive film. The second photosensitive film is photosensitive to the second electromagnetic spectrum whereby exposure by the second electromagnetic spectrum will activate the second photosensitive film but not the first photosensitive film and exposure by the first electromagnetic spectrum will activate unmasked portions of the first photosensitive film.
In accordance with another aspect of the present invention, a circuit structure is provided that includes a substrate and a positive photoresist film on the substrate. The positive photoresist film is photosensitive to a first electromagnetic spectrum and anti-reflective of a second electromagnetic spectrum that differs from the first electromagnetic spectrum. A photosensitive film is on the positive photoresist film. The photosensitive film is photosensitive to the second electromagnetic spectrum whereby exposure by the second electromagnetic spectrum will activate the photosensitive film but not the positive photoresist film and exposure by the first electromagnetic spectrum will activate unmasked portions of the positive photoresist film.
In accordance with another aspect of the present invention, a method of manufacturing is provided that includes forming a first photosensitive film on a substrate. The first photosensitive film is photosensitive to a first electromagnetic spectrum but anti-reflective of a second electromagnetic spectrum that differs from the first electromagnetic spectrum. A second photosensitive film is formed on the first photosensitive film. The second photosensitive film is photosensitive to the second electromagnetic spectrum whereby exposure by the second electromagnetic spectrum will activate the second photosensitive film but not the first photosensitive film and exposure by the first electromagnetic spectrum will activate unmasked portions of the first photosensitive film.